1. Field of the Invention
This invention relates to optical devices for use in, for example, cameras, telescopes, microscopes and various kinds of optical measuring instruments, and more particularly to beam splitters and optical devices using the same in optical systems of such instruments.
2. Description of the Prior Art
The prior known beam splitters are exemplified in FIGS. 1A to 1C. The beam splitter of FIG. 1A includes a half-reflection mirror HM and is of the split-amplitude type. The entering light beam L1 is split into two parts L2 and L3 at a prescribed ratio. Thus, there is a disadvantage that both exiting beams become darker.
In FIG. 1B, a partial mirror PM is positioned in the path of a portion of the beam L1 to split off a wave front of light. In this case too, both fields of view become darker.
In FIG. 1C, the beam L1 is split by a slidable mirror SM positioned at an angle of inclination to the beam. Since a space must be created for the slidable mirror to occupy when retracted, the use of this beam splitter is disadvantageous when trying to minimize the size of the optical device.